In a time-of-flight (TOF) mass spectrometer (MS), ions are accelerated with substantially constant energy. It is understood that the light ions will travel faster than the heavier ions. The time an ion travels a fixed distance is measured. Accordingly, an ion's mass can then be calculated from this time of flight.
If the distance travelled by the ions is short, then ions of similar mass have substantially similar (short) flight times. In some instances, these similar times can result in ions of similar masses being indistinguishable from each other, which yields low resolution results.
To increase the resolution from this phenomenon, it is known to increase the distance (thereby the flight time) for the ions to travel. In such an implementation, the total time of flight for all ions is increased. This longer flight time, while increasing resolution, can have shortfalls as it acts to limit how frequently the mass spectrometer can accelerate groups of ions. This, in turn, limits sensitivity. It places a lower bound on the concentrations that can be detected.
In a traditional, non-multiplexed TOF MS, a group of ions is accelerated. Then the MS waits until all of the ions in the group have arrived at the detector (the end of the flight path). Only then can the next group of ions be accelerated. Long flight times limit how frequently ions can be accelerated, resulting in decreased sensitivity.
Generally
Implementations of multiplexed high resolution mass spectrometry are disclosed to allow the mass spectrometer to avoid waiting for all ions from one group to arrive at the detector before accelerating a next group thereby facilitating ions from many different groups to be simultaneous in flight. As a result, this increases the number of ions that traverse the flight path in a given amount of time.
In a traditional mass spectrum system, the data reported by the detector from such an arrangement is not recognizable as the data is a shifted sum of mass spectra from the individual ion groups, referred herein as a “multiplexed spectrum”. By multiplexing the timing of the groups of accelerated ions as discussed, one can thereafter utilized methods to convert this multiplexed spectrum into traditional mass spectrum, which will be referenced herein as demultiplexing. In summary, multiplexing in the mass spectrometer and thereafter demultiplexing in software facilitates the system to simultaneously maintain high resolution & high sensitivity. Additional, the disclosed implementations can also improve spectral selectivity. In other words, traditional mass spectra can contain artifacts from stray ions or spontaneous detector emissions whereas application of implementations of demultiplexing can confirm a presence of a spectral peak thereby effectively filtering such spectral artifacts.
Traditional Mass Spectrometer
A chart illustrating exemplary results from a traditional time-of flight mass spectrometer is provided at FIG. 1. As illustrated, the results depict a mass spectrum that contains information meaningful to an analytical chemist. The locations of the spectral peaks correspond to the time of flight of each ion and to the measured mass of each ion received by the detector.